In most printers, paper is advanced without any feedback regarding the actual paper position. Instead, it is assumed that the paper advances through the printer in direct relation to the motion of the printer's advance mechanism. References to the paper advance being "closed loop" or "servo-controlled" apply to the paper advance mechanism-not to the paper itself.
Open loop paper advance has worked well because the properties of paper are well understood and the required precision of the paper motion have not been great. With increased requirements for positioning accuracy, however, variations in media response and inaccuracies from drive roller eccentricity are contributing to a larger percentage of total paper advance error. As a result, efforts have been made to truly close the positioning loop by measuring the movement of the paper itself during operation of the printer. However, this technology is currently quite complex and prohibitively expensive.
Nevertheless, there is a pressing need for some method to calibrate a printer's media advance mechanism in a way that accounts for variations in the printer's components, variations in the printer's environment, and variations in the print media. The invention described herein meets this need.